Japanese authorities are ready to act against excessive yen rises, the government’s top spokesman said on Friday, issuing a fresh warning to markets against recent yen gains that could hurt the country’s export-reliant economy. The dollar fell to a nearly four-week low of 100.10 yen on Thursday after the U.S.

“The government hopes to keep watching currency market moves ever more carefully and if such moves persist, will be ready to take necessary action,” he said. Economy Minister Nobuteru Ishihara also told reporters on Friday he wants to closely watch yen moves and analyse its potential economic impact.

Japanese policy-makers say they do not have a specific level they have in mind as they try to talk the market out of pushing up the yen, but many traders see 100 to the dollar as authorities’ line in the sand.